Pressure relief valves are widely used in motor vehicles to relieve air pressure surges or peaks in the passenger compartment which result for example, when the doors are slammed shut or an airbag is inflated. The valves generally comprise a simple rigid frame or housing which mounts in an aperture in a vehicle body panel. A wall of the housing extending generally parallel to the vehicle body panel has an opening through which air may pass. A valve element in the form of a normally flexible plastic flap is connected to the housing to overlie the opening in the housing wall. The valve element opens relative to the housing to uncover the opening to relieve air pressure surges. The pressure relief valve may include louvers that cover the valve element to make the pressure relief valve more visually pleasing.